"Fine Grained Polysilicon and its Application to Planar Pressure Transducers", H. Guckel et al., Transducers '87, pp. 277-282, describes a process for producing pressure sensors by surface micromechanics in which three-dimensional sensor structures, such as thin membrane, tongue or bridge structures, are produced in a succession of thin films deposited on a monocrystalline silicon substrate. The deflectable or deformable sensor structures are produced by first applying a structured silicon layer to the substrate, then depositing a polysilicon layer on top of that. Structuring the polysilicon layer and lateral undercutting, in the process of which the structured silicon oxide layer is removed, exposes the sensor structure in the polysilicon layer. This article also studies the effects of various parameters of the production process on the material properties of the sensor structure. The mode of operation and reliability of such sensors are decisively dependent on the properties, such as the modulus of elasticity, of the material from which the deflectable or deformable components of the sensor are made.
German Patent Application P 40 22 495.3 filed fall 1990, entitled Mikromechanischer Drehratensensor, the publication date of which does not predate the present application, also discloses a process for producing sensor structures in three-layer silicon wafers, in which retaining webs for a vibratable seismic mass are formed in the two outer layers.